1. Field of the Invention
The present invention relates to electrical circuits for detecting and displaying the availability to, and use of power by, a load.
2. Related Art
There are many settings in which knowing whether a control element, such as a solenoid, motor, pump, or compress, is running or not, is of great importance. For example, boats have a bilge pump to get rid of any water that may accumulate in the bilge. The pump is usually placed in the lowest part of the bilge and controlled by a float switch. It is difficult to know whether the pump is running or not. One solution to this problem has been the pilot light shown in FIG. 1.
FIG. 1 shows a typical pilot light that indicates when the on/off switch is in the on position and power is available to the load. However, this pilot light does not show whether the float is in the active position or whether the pump is running.
FIG. 2 shows an improvement of the pilot light shown in FIG. 1, indicating when the float is active and power is available. However, this pilot light still does not show whether the pump is running. Further, the wires that connect the pilot light to the pump must be capable of carrying the breaker current rating, and the wires must be run to the pump, which can be a long distance. FIG. 3 uses a second pilot light to indicate whether power is available. The other characteristics are the same as for the pilot light of FIG. 2.
Bi-color light-emitting diodes have two light-emitting diodes inside one lens package, usually red and green. They can come in 3-pin or 2-pin packages. The E231 and E292 models are 3-pin packages. The pins of the E292 are a red cathode, a green cathode, and a common anode. With the anode voltage greater than the red cathode voltage by 2.2 volts, the red light-emitting diode will light up; with the anode voltage greater than the green cathode voltage by 2.2 volts, the green light-emitting diode will light up. The pins of the E231 are a red anode, a green anode, and a common cathode. With the red anode voltage greater than the cathode voltage by 2.2 volts, the red light-emitting diode will light up; with the green anode voltage greater than the cathode voltage by 2.2 volts, the red light-emitting diode will light up. Reed switches, which are generally inexpensive devices, close in response to a magnetic field. They generally consist of a pair of flexible reeds made of a magnetic material sealed in a glass tube filled with inert gas. The reeds extend outside the tube in opposite directions, and overlap inside the tube but are separated by a small gap. Because of the gap, the reeds constitute an open circuit. Application of a magnetic field to the reed switch causes both reeds to be magnetized. If the magnetic attracting force overcomes the resistive force caused by the elasticity of the reeds, the reeds come into contact, closing the circuit. The magnetic field can be generated by a magnet or a current flowing through a coil nearby. Once the magnetic field is removed, the reeds separate, and the circuit is opened.
Field-effect transistors (FETs) have three terminals: a gate, a source, and a drain. Conduction in the channel between the source and the drain is controlled by an electric field applied to the gate; the resistance between the source and the drain is determined by the voltage difference between the gate and the source. In N-channel FETs, the voltage at the gate must be greater then the voltage at the source to allow current to flow between the source and the drain.